High frequency circuit

Abstract

A high frequency circuit includes a transistor having an input electrode that inputs a high frequency signal and an output electrode that outputs the high frequency signal, a transmission line that is connected to any one of the input electrode and the output electrode, and transmits the high frequency signal, a coupling line electrically separated from the transmission line to an extent that an electromagnetic field coupling is enabled with the transmission line, and a resonance circuit that is connected between a first end of the coupling line and a reference potential, and minimizes an impedance between the first end and the reference potential at a resonance frequency.

What is claimed is: 
     
       1. A high frequency circuit comprising:
 a transistor having an input electrode that inputs a high frequency signal and an output electrode that outputs the high frequency signal; 
 a transmission line that is connected to any one of the input electrode and the output electrode, and transmits the high frequency signal; 
 a coupling line electrically separated from the transmission line to an extent that an electromagnetic field coupling is enabled with the transmission line; and 
 a resonance circuit that is connected between a first end of the coupling line and a reference potential, and minimizes an impedance between the first end and the reference potential at a resonance frequency, and 
 wherein the resonance frequency of the resonance circuit is lower than an operating frequency band of the high frequency circuit. 
 
     
     
       2. The high frequency circuit as claimed in  claim 1 , further comprising:
 a resistance element; 
 wherein a first end of the resistance element is connected to a second end of the coupling line, a second end of the resistance element is connected to the reference potential, and a resistance value of the resistance element is ½ times or more and twice or less a characteristic impedance of the coupling line at a center frequency of the operating frequency band of the high frequency circuit. 
 
     
     
       3. The high frequency circuit as claimed in  claim 1 , further comprising:
 an input terminal that inputs the high frequency signal; and 
 a matching circuit that matches an input impedance of the input terminal with an input impedance of the input electrode; 
 wherein a first end of the transmission line is connected to the matching circuit, and a second end of the transmission line is connected to the input electrode. 
 
     
     
       4. The high frequency circuit as claimed in  claim 1 , further comprising:
 an output terminal that inputs the high frequency signal; and 
 a matching circuit that matches an output impedance of the output electrode with an output impedance of the output terminal; 
 wherein a first end of the transmission line is connected to the output electrode, and a second end of the transmission line is connected to the matching circuit. 
 
     
     
       5. The high frequency circuit as claimed in  claim 1 , wherein
 the input electrode is a gate and the output electrode is a drain. 
 
     
     
       6. The high frequency circuit as claimed in  claim 1 , wherein
 at the resonance frequency of the resonance circuit, a stability coefficient of the high frequency circuit when the coupling line and the resonance circuit are not provided is less than 1. 
 
     
     
       7. The high frequency circuit as claimed in  claim 1 , wherein
 the resonance frequency of the resonance circuit is ½ or less of the operating frequency band of the high frequency circuit or ⅓ or less of the operating frequency band of the high frequency circuit. 
 
     
     
       8. The high frequency circuit as claimed in  claim 1 , wherein
 the resonance circuit includes an inductor and a capacitor connected in series between the first end of the coupling line and the reference potential.